A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simple network architecture. An LTE system also provides seamless integration to older wireless networks, such as Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), and Universal Mobile Telecommunication System (UMTS). In LTE systems, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) communicating with a plurality of mobile stations, referred as user equipments (UEs).
Enhancements to LTE systems are considered by the third Generation Partnership Project (3GPP) so that they can meet or exceed International Mobile Telecommunications Advanced (IMT-Advanced) fourth generation (4G) standard. One of the key enhancements is to support bandwidth up to 100 MHz and be backwards compatible with the existing wireless network system. Carrier aggregation (CA), where two or more component carriers (CCs) are aggregated, is introduced into LTE-Advanced systems to improve overall system throughput.
Multimedia Broadcast and Multicast Service (MBMS) is a broadcasting service offered via existing GSM and UMTS cellular networks. Recently, evolved MBMS (E-MBMS) has been introduced in the LTE specification for broadcasting or multicasting TV, films, and other information such as overnight transmission of newspapers in a digital form. To facilitate MBMS in LTE systems, a multicast control channel (MCCH) is used for the transmission of MBMS control information in each MBMS Single Frequency Network (MBSFN) area, and a multicast traffic channel (MTCH) is used for the transmission of user traffic to UEs receiving MBMS data packets. MBMS has the major benefit that the network infrastructure already exists for mobile network operators and that deployment can be cost effective compared with building a new network for the service. The broadcast capability enables to reach unlimited number of users with constant network load. The broadcast capability also enables the possibility to broadcast information simultaneously to many cellular subscribers, such as emergency alerts.
An important feature of a mobile wireless system such as LTE is the support for seamless mobility across eNBs and the entire network. Fast and seamless handover (HO) is particularly important for delay-sensitive services such as VoIP. Likewise, MBMS service continuity is also important for MBMS user experience. The mobility of a UE should affect MBMS service reception as less as possible. However, there is no network-assisted MBMS service continuity supported by the current LTE specification (e.g., in LTE Rel-9). Before any network solution is available, MBMS service continuity can only be supported by UE-centric solution. Furthermore, with the addition of carrier aggregation (CA) in LTE-A systems, and with the possibility of network base stations (e.g., eNBs) covered by multiple MBSFN areas, it is foreseeable that an eNB can be associated with more than one MBSFN areas. UE-centric solution for MBMS service continuity under such scenario is also desirable.